adb: Remove the obsolete include path to ext4_utils.

Since commit 8ad80763e4b3bdcd80d16c63f03b19eb9df989b2 has removed
'#include "ext4_sb.h"', there's no more reference to ext4_utils headers.

Test: `mmma system/core/adb`

Change-Id: I7ca1a6e91f1e0de84238c2a7facbebe9600a3d87
diff --git a/adb/Android.mk b/adb/Android.mk
index 0114ca3..9466bee 100644
--- a/adb/Android.mk
+++ b/adb/Android.mk
@@ -324,7 +324,6 @@
 LOCAL_FORCE_STATIC_EXECUTABLE := true
 LOCAL_MODULE_PATH := $(TARGET_ROOT_OUT_SBIN)
 LOCAL_UNSTRIPPED_PATH := $(TARGET_ROOT_OUT_SBIN_UNSTRIPPED)
-LOCAL_C_INCLUDES += system/extras/ext4_utils
 
 LOCAL_SANITIZE := $(adb_target_sanitize)
 LOCAL_STRIP_MODULE := keep_symbols